1. Field of the Invention
The present invention relates to 1,2-polybutadiene compositions curable to flame retarded resin materials and to cured flame retarded 1,2-polybutadiene resin materials. The cured products in accordance with the invention exhibit an improved flame retardancy performance over the cured 1,2-polybutadiene, while retaining desirable properties of the cured 1,2-polybutadiene, such as high heat resistance and excellent dielectric properties. Preferred cured products in accordance with the invention further exhibit a thermal expansion coefficient lower than that of the cured 1,2-polybutadiene.
2. Description of the Prior Art
Because of their excellent electrical properties, in particular dielectric properties, and excellent resistances to heat, water and chemicals, 1,2-polybutadiene and cured products thereof are widely used in parts of electrical and electronic devices and equipment as a substrate of a printed circuits board, a coating resin for printed circuits, a molding compound or an insulating varnish. Nevertheless, 1,2-polybutadiene and cured products thereof have a drawback in that they are readily burnable since their molecules are solely composed of hydrogen and carbon atoms.
For parts of electrical and electronic devices and equipment, a certain level of flame retardancy performance has been recently required as a standard, and the flame retardation of 1,2-polybutadiene has now been one of the most important problems in the art. Most of the prior art approaches for the flame retardation of 1,2-polybutadiene are unsatisfactory in that a sufficient flame retardancy performance is not achieved or can only be achieved with the sacrifice of desirable properties inherently possessed by 1,2-polybutadiene. For example, methods for the flame retardation of 1,2-polybutadiene based on the use of addition-type flame retardants, such as hexabromobenzene, decabromodiphenyl ether and triphenyl phosphate, optionally together with auxiliary flame retardants, such as antimony trioxide and triphenylantimony, result not only in impairment of desirable dielectric properties and heat resistance inherently possessed by 1,2-polybutadiene, but also in undesirable bleeding out of the flame retardant to the surfaces of the cured resin.
On the other hand, methods for the flame retardation of 1,2-polybutadiene based on the use of reactive flame retardants, such as 2,4,6-tribromophenylacrylate or -methacrylate, are proposed in Japanese Patent Laid-open Specifications 50-30,019, published on Mar. 26, 1975, and 50-32,241, published on Mar. 28, 1975, as well as in examined Japanese Patent Publication 53-21,433, published on July 3, 1978. By these methods, however, the flame retardancy performance is not durable although the initial level of flame retardancy performance is satisfactory. Furthermore, while the desirable dielectric properties of 1,2-polybutadiene can be retained, the high heat resistance inherently possessed by 1,2-polybutadiene is adversely affected.